Lagrangian-Style Subsurface Current Measurements Through Tracking of Subsurface Drifters

Abstract. A physically-based technique for interpolating external magnetic field disturbances across large spatial areas can be achieved with the Spherical Elementary Current System (SECS) method using data from ground-based magnetic observatories. The SECS method represents complex electrical current systems as a simple set of equivalent currents placed at a specific height in the ionosphere. The magnetic field recorded at observatories can be used to invert for the electrical currents, which can subsequently be employed to interpolate or extrapolate the magnetic field across a large area. We show that, in addition to the ionospheric currents, inverting for induced subsurface current systems can result in strong improvements to the estimate of the interpolated magnetic field. We investigate the application of the SECS method at mid- to high geomagnetic latitudes using a series of observatory networks to test the performance of the external field interpolation over large distances. We demonstrate that relatively few observatories are required to produce an estimate that is better than either assuming no external field change or interpolation using latitudinal weighting of data from two other observatories.

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Structure and dynamics of the Pacific North Equatorial Subsurface Current

Scientific Reports ◽

10.1038/s41598-020-68605-y ◽

2020 ◽

Vol 10 (1) ◽

Cited By ~ 1

Author(s):

Xiang Li ◽

Ya Yang ◽

Rui Li ◽

Linlin Zhang ◽

Dongliang Yuan

Keyword(s):

Structure And Dynamics ◽

The Pacific ◽

Subsurface Current

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Influence of surface waves on subsurface current measurements in shallow water1

Limnology and Oceanography ◽

10.4319/lo.1976.21.4.0611 ◽

1976 ◽

Vol 21 (4) ◽

pp. 611-616 ◽

Cited By ~ 31

Author(s):

David Halpern ◽

R. Dale Pillsbury

Keyword(s):

Surface Waves ◽

Subsurface Current

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The calving and drift of iceberg B-9 in the Ross Sea, Antarctica

Antarctic Science ◽

10.1017/s0954102090000335 ◽

1990 ◽

Vol 2 (3) ◽

pp. 243-257 ◽

Cited By ~ 40

Author(s):

Harry (J.R.) Keys ◽

S.S. Jacobs ◽

Don Barnett

Keyword(s):

Ocean Circulation ◽

Ross Sea ◽

Maximum Velocity ◽

Open Water ◽

Ice Thickness ◽

Ice Shelf ◽

East Central ◽

North West ◽

Ross Ice Shelf ◽

Subsurface Current

Major rifts is the Ross Ice Shelf controlled the October 1987 calving of the 154 × 35 km “B-9” iceberg, one of the longest on record. The 2000 km, 22 month drift of this iceberg and the quite different tracks of smaller bergs that calved with it have extended our understanding of the ocean circulation in the Ross Sea. B-9 initially moved north-west for seven months until deflected southward by a subsurface current which caused it to collide with the ice shelf in August 1988. It then completed a 100 km-radius gyre on the east-central shelf before resuming its north-westerly drift. Based upon weekly locations, derived from NOAA-10 and DMSP satellite and more frequent ARGOS data buoy positions, B-9 moved at an average speed of 2.4 km day−1 over the continental shelf. It was not grounded there at any time, but cast a large shadow of open water or reduced ice thickness during the austral winters. B-9 was captured by the continental slope current in May 1989, and attained a maximum velocity of 13 km day−1 before breaking into three pieces north of Cape Adare in early August 1989.

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Three‐dimensional terrain corrections for mise‐à‐la‐masse and magnetometric resistivity surveys

Geophysics ◽

10.1190/1.1441579 ◽

1984 ◽

Vol 49 (10) ◽

pp. 1718-1729 ◽

Cited By ~ 23

Author(s):

G. L. Oppliger

Keyword(s):

Surface Charge ◽

Charge Distribution ◽

Electric Fields ◽

Current Source ◽

Three Dimensional ◽

Solution Technique ◽

Surface Integral ◽

Surface Charge Distribution ◽

Terrain Corrections ◽

Subsurface Current

Three‐dimensional modeling of topographic effects in mise‐à‐la‐masse and magnetometric resistivity surveys is accomplished using the surface integral equation method. The technique provides a means for (1) analyzing these effects on earth models of homogeneous conductivity; and (2) removing terrain effects from field data. A new method combining current source images with surface charge is developed to treat the electric field boundary conditions at the air‐earth interface. The method uses an image of each subsurface current source positioned above the surface, so as to induce a surface charge distribution which approximately cancels the charge distribution induced by the subsurface current source. The resulting residual surface charge distribution varies spatially more gradually than either of the original charge distributions, and hence may be represented accurately on a coarsely segmented model surface with simple basis functions. The topographic surface is modeled by a finite number of facets, each with constant slope and surface charge density. Charge values are obtained with an iterative solution technique. Surface electric fields are calculated from the surface charge distribution, current sources, and images. The magnetic field is found by evaluating a surface integral involving surface slopes and electric fields. The numerical solution is verified by comparisons with dipole‐dipole resistivity results from a two‐dimensional finite‐element model of a valley, and with analytic solutions for the magnetic fields over a dipping interface. Methods for terrain correcting mise‐à‐la‐masse and magnetometric resistivity data are demonstrated with examples using actual field measurements. The results of this study show that (1) rugged topography can significantly distort measurements in mise‐à‐la‐masse and magnetometric resistivity surveys; and (2) the described modeling technique provides an effective means of calculating terrain corrections for both the mise‐à‐la‐masse and magnetometric resistivity methods over complex three‐dimensional topography.

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